A delicately drawn study of the monument to Russian Tsar Nicholas I in St Petersburg's landmark Isaac's Square will go under the hammer at Christie's Russian art sale in mid October in London.

The drawing penned by celebrated French architect Auguste Montferrand has been estimated at $144,000.

Montferrand made a name for himself as the creator of two of St. Petersburg's historic monuments – the legendary Saint Isaac's Cathedral and the Alexander Column.

The bronze equestrian monument to Nicholas I in the heart of the city turned out to be the architect's last work. It was commissioned by Tsar Alexander II back in 1856, and was completed a year after Montferrand died.

According to Christie's, Montferrand's drawing of the six-meter statue is a “discovery of great importance.”

It will be sold together with a portfolio of the master’s original drawings of the unique structure of the monument, which was the first equestrian statue in the world equipped with only two support points.